I am in the camp that in a GDI engine that using synthetic 10W30 oil with it's lower NOACK and lower VII's content would be best for a GDI engine (in terms of reducing intake valve depositis) ? Conversely , recent updated tech information may prove such a belief may be a myth and no longer valid : 1) Updated information suggests a lower NOACK oil is not a significant contributor to GDI intake valve deposits . 2) High amounts of VII's are a contributor to intake valve deposits , HOWEVER newer formula VII's are of a composition now to where that is not as much of an issue as with previous earlier SN rated oils and before . Better oil formulas (better base stocks , improved VII's etc.) in SP rated oils suggest that using a good SP rated synthetic D1 / Gen 3 5W30 oil may be best in a GDI engine where both 10W30 and 5W30 were previously recommended in the owner's manual . Lastly , in GDI engines which do not also inclide dual GDI / PFI injectors - it would still be a good practice to runa intaake valve cleaner (i.e. CRC) every 10K miles (or every other OCI along with top tier gas for optimum engine performance ... More capable folks here such as Gokhan , Molekule , etc. can weigh in on key performance indicators for oil / GDI engines I allude to in this post .
The best way to prevent GDI deposits is by having dual injection. While that apparently wasn't the original reason Toyota was doing it, Ford is now using this as well and I expect we'll see others follow suit.
There are two schools of thought about IVD's:
1. That volatile compounds (so, not VII's) like lighter fractions from the base oil blend, flash off and make their way into the intake tract through the PCV, ultimately forming deposits on the back of the valves.
2. That oil mists produced during operation make their way through the same plumbing and the various components of these mists produce deposits.
The rationale behind focusing on Noack is #1, with #2, you accept that oil will be introduced into the intake regardless and are looking at reducing the concentration of the components that seem most inclined to form deposits.
This strikes me as akin to trying to use 10W-60 to delay rod bearing failure. It's still going to happen, but maybe it happens a bit slower.
One of the biggest drivers of volatilized compounds, and probably the mist angle too, would be fuel dilution, which varies considerably between marques and engine designs. If >5% of your sump is gasoline, clearly, that's going to present as a far greater propensity for volatilized compounds to flash off and get introduced to the intake tract via the PCV.